Hydraulically actuated apparatus for the mechanical splitting of rock

ABSTRACT

An apparatus for mechanically breaking up or splitting rock. Apparatus of this type may consist of a cylinder block having a hydraulically actuatable, longitudinally movably piston arranged therein, with this piston acting, by way of a slider wedge which is connected to the piston rod, on headed presser cheeks which can be inserted in drill holes and laterally moved, the presser cheeks having an obliquity which corresponds to the inclination of the slider wedge, and with the head of one of the presser cheeks being U-shaped and having arms which engage opposite sides of the slider wedge. By arranging for the heads of the presser cheeks to engage one in the other, all axial displacements or axial loads of one of the presser cheeks being transmitted, uniformly and in the same direction, to the other presser cheek, the U-shaped head of one of the presser cheeks being radially shiftably suspended in a hollow member and engaging round a reduced neck portion of the head, which is T-shaped in longitudinal cross-section, of the other presser cheek.

United States Patent [191 Darda [451 July 15, 1975 HYDRAULICALLY ACTUATED APPARATUS FOR THE MECHANICAL SPLI'I'IING OF ROCK [76] Inventor: Helmut Darda, lm Ta], D-77l2 Blumberg, Germany [22] Filed: July IS, 1974 [2|] App]. No.: 489,032

[30] Foreign Application Priority Data July l6, l973 Germany 2336063 [52] US. Cl. 299/22; 299/23 [51] Int. Cl. EZIC 37/02 [58] Field of Search 299/22, 23; l25/23 R [56] References Cited UNITED STATES PATENTS 3,558,l9l l/l97l Fletcher et al 299/22 3,791,698 2/1974 Darda 299/23 Primary Examiner-Ernest R. Purser Attorney, Agent, or FirmWaters, Schwartz & Nissen [57] ABSTRACT An apparatus for mechanically breaking up or splitting rock. Apparatus of this type may consist of a cylinder block having a hydraulically actuatable, longitudinally movably piston arranged therein, with this piston acting, by way of a slider wedge which is connected to the piston rod, on headed presser cheeks which can be inserted in drill holes and laterally moved, the presser cheeks having an obliquity which corresponds to the inclination of the slider wedge, and with the head of one of the presser cheeks being U'shaped and having arms which engage opposite sides of the slider wedge. By arranging for the heads of the presser cheeks to engage one in the other, all axial displacements or axial loads of one of the presser cheeks being transmitted, uniformly and in the same direction, to the other presser cheek, the U-shaped head of one of the presser cheeks being radially shiftably suspended in a hollow member and engaging round a reduced neck portion of the head, which is T-shaped in longitudinal cross-section, of the other presser cheek.

15 Claims, 8 Drawing Figures SHEEI 2 I4 8 6 mam u m I HYDRAULICALLY ACTUATED APPARATUS FOR THE MECHANICAL SPLITTING OF ROCK FIELD OF THE INVENTION The invention relates to an apparatus for mechanically breaking up or splitting rock. Apparatus of this type may consist of a cylinder block having a hydraulically actuatable, longitudinally movably piston ar ranged therein, with this piston acting, by way of a slider wedge which is connected to the piston rod, on headed presser cheeks which can be inserted in drill holes and laterally moved, the presser cheeks having an obliquity which corresponds to the inclination of the slider wedge, and with the head of one of the presser cheeks being U-shaped and having arms which engage opposite sides of the slider wedge.

The presser cheeks are either directly connected to the cylinder block, or are indirectly connected thereto by means of a hollow member which is detachably mounted on the cylinder block. In the latter instance, the heads of the presser cheeks lie within the hollow member.

Forces of the order of magnitude of 300 tons and more can be generated by means of apparatus which is constructed in this manner, whereby such apparatus becomes of considerable practical use in the breaking up or splitting clumps of rock without the use of explosives. In spite of the large pressures per unit surface area, the presser cheeks and the slider wedge only have diameters of the order of magnitude up to 50 mm and, consequently, the drill holes can be made inexpensively and relatively easily.

DISCUSSION OF THE PRIOR ART Rock splitting apparatus of this type is disclosed in detail, for example, in German Published Pat. Application No. l,249,l94, and has been found excellent in use. For example, this apparatus is used in quarries, on sites in which rocks are processed, in mines, and also for demolition work in the fields of building construction and civil engineering. This apparatus is so constructed that the relatively slender presser cheeks and slider wedge, the suspension for the presser cheeks and the piston rod which is connected to the slider wedge, can all withstand substantial bending stresses.

However. certain CIlfflCUIlICS may arise if the loads sustained by the two presser cheeks greatly differ, so that the cylinder block, which is rigidly connected to the presser cheeks, assumes an inclined position relative to the insert. Asymmetry of this kind occurs, for example, when the rock is only broken up in the vicinity of one of the presser cheeks, while the rock in the vicinity of the other presser cheek has not yet been broken up. Under these circumstances the cylinder block will be literally bent in the direction of the portion of the rock which has not yet been broken or split; this being due to asymmetrical loading or caused by a clump of rock being lifted. The above-mentioned rockbreaking apparatus is so constructed that an angle of inclination between cylinder block and insert presser cheeks of up to is permissible. When, however, the angle of inclination is greater, the infeed of fluid pressure medium must be interrupted, and a further rockbreaking apparatus be brought into service in the vicinity of the drill hole, although the first rock breaking apparatus still has power available.

In order to prevent a dangerous inclination of the cylinder block relative to the presser cheeks, in the case of asymmetrical loading it has previously been proposed to arrange at least one presser cheek so that it is axially shiftable relative to the cylinder block or to the tubular member connected to the cylinder block, and to so suspend the presser cheeks that, even in the case of asymmetrical loading of the presser cheeks, the resultant of the counteracting forces which act on these presser cheeks act approximately along the axis of the slider wedge. In accordance with the above-mentioned proposal it is possible to mount one or both of the presser cheeks so as to be axially shiftable. In the case of the first of these alternatives only one presser cheek is rigidly connected to the hollow member and the pressure exerted by the slider wedge must, in order to avoid counteracting forces which result in the dangerous inclination of the cylinder block relative to the insert, act on the same point as the pulling force which is effective at the axis of the non-shiftable presser cheek. Previously, this has been achieved by giving the head of the axially non-shiftable presser cheek, which is suspended in the hollow member, a Ushaped cross-section, and by arranging for the arms of the head of this presser cheek to straddle the slider wedge, these arms of the said U-shaped head being supported by inwardly projecting shoulders of the hollow member.

According to the second of these known alternatives. where both presser cheeks are arranged so as to be axially shiftable within the hollow member and the pulling forces are taken up by tie-bars and guide-bars which are rigidly connected to the cylinder block, the presser checks are radially and axially shiftable in these tie-hars and guide bars, and the outer end surfaces of these presser cheeks are supported on a strip or web which interconnects the tie bars.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide apparatus of the abovemcntioned type, in which the forces which act on the presser checks are so transmitted, when the presser cheeks are asymmetrically loaded, so as to prevent an inclination of the cylinder block. With a view to solving this problem a different solution from that of the above-mentioned prior proposal is adopted. According to this novel approach to the problem the two presser cheeks are no longer freely axially shiftable. Notwithstanding the foregoing, the equipment is still of simple and sturdy construction and relatively inexpensive to manufacture.

This object is achieved, in an apparatus of the type described above, by arranging for the heads of the presser checks to engage one in the other, all axial displacements or axial loads of one of the presser cheeks being transmitted, uniformly and in the same direction, to the other presser cheek, the U-shaped head of one of the presser cheeks being radially shiftably suspended in a hollow member and engaging round a reduced neck portion of the head, which is T-shaped in longitudinal cross-section, of the other presser cheek.

An important advantage of the apparatus according to the invention resides in the fact that when one of the presser cheeks is forced in a direction tending to move it axially relative to the other presser cheek this attempted" movement is immediately transmitted by reason of the way in which the parts engage one in the other to the other presser cheek. Different surfaces come into mutual contact according to the direction of the particular relative displacement concerned, and the transmission of force or of movement applies to all movements of the different presser cheeks.

As the head portion of one of the presser cheeks engages opposite sides of the slider wedge, the wall thickness of the presser cheek can, for a given strength, be decreased in this area. This results in a saving in space and, for this reason, it is possible to use a slider wedge having a steeper inclination so that a greater separation of rock may be achieved for a given amount of axial displacement of the slider wedge. Also, the head of the presser cheek which is U-shaped in cross-section enables the slider wedge to be satisfactorily guided.

Further, it is possible to support a T-shaped portion of the head of one of the presser checks on the head of the other presser cheek with a disc, which is interposed, with the provision of play, between an end face of a guide sleeve, which serves to guide the piston rod, and the T-shapcd portion of the head of said one of the presser cheeks.

In this embodiment the transmission of force takes place in the case of a relative displacement of the presser checks in one direction by way of the intermediate disc, the latter being intentionally inserted with provision for play, so that the slider wedge can be swivelled together with the presser check which straddles it.

According to another embodiment of the invention, the T-shaped portion of the head abuts against an axially rearwardly offset portion of the end face of the guide sleeve. This dclimits or defines the axial position of the associated presser cheek, because the T-shaped head portion is located or fixed between the intermediate disc and the end face of the guide sleeve.

According to a further embodiment. the reduced neck portion of the head can abut, by way ofa shoulder located at the base of this neck portion, the undersurface of the head of the other presser cheek.

By virtue of this form of construction, and particularly in conjunction with various other previously mentioned features of the invention. the two heads of the presser cheeks can, in an extremely simple manner, engage one in the other in a form-locking and forcelocking connection.

Conveniently, the presser cheek having the T-shaped head may, by means of a lug which lies under this head, about the hollow member, and in this way be radially located or fixed.

The lug provides a radial reference point, so that the surface of the presser check will always, at the level of the lug, lie at the same radial distance from the hollow member or from the longitudinal axis.

According to a further embodiment. the slider wedge and the lower portions of the presser cheeks are symmetrically constructed. lt is also possible to give the slider wedge and the presser cheeks an asymmetrical shape.

An apparatus according to the invention is highly versatile and enables the use ofa wide variety of slider wedges and presser checks. in the case of an asymmetrical mode of construction, the presser checks should, conveniently, be so suspended that the resultant of the counteracting forces acting on the presser checks should act, even in the case of asymmetrical loading of the presser cheeks, approximately along the axis of the slider wedge.

Preferably, the sliding surface of the presser cheek having a U-shaped head should be given a greater angle of inclination, relative to the longitudinal axis, than the sliding surface of the other presser cheek. Apart from the special shape given to the presser cheeks and to their heads, this results in a better distribution of the operative forces.

According to a modification, the slider wedge is pivotably secured in the piston rod by means of a transverse pin. This transverse pin may, by way of its ends which extend laterally from the slider wedge, engage in elongate holes of the piston rod. It may be envisaged that the elongate holes will, while the slider wedge is being advanced, result in abutment between the piston rod and the slider wedge over a relatively large surface area.

Due to the way in which the slider wedge is rockingly suspended from the piston rod, the apparatus is extremely flexible in use. For example, in the case of asymmetrical construction, only one of the presser checks is radially shifted, while the other presser cheek cannot be radially shifted due to the abutment of the lug on the hollow member, Further, the slider wedge can, by reason of its pivotal form of suspension, be radially shifted, together with the presser cheek which straddles it, for the purpose of withdrawing the other pressure cheek, after it has been suitably turned through an angle of by its head through the arms of the head of the other presser cheek and so withdrawing it from the apparatus. It is also in this way possible to quickly and simply repair this presser cheek or exchange it (for example by a thicker presser check). As the transversee pin lies in an elongate hole, it is possible to effect contact of large surface areas of the end faces of these parts when moving the piston rod and, consequently, the slider wedge outwardly. The sides of the transverse pin only engage in the other end face of the elongate hole when the piston rod is, together with the slider wedge, being retraced, i.e., moved inwardly, so that the slider wedge can be returned. According to a further modification, the underface of the hollow memher is covered off by a resilient impact disc which at least partially surrounds the presser cheeks and continuously holds the latter in contact with the slider wedge. While the resilient impact disc affords mechanical protection for the parts lying within the hollow member, this disc at the same time constitutes a resiliently yielding abutment surface, which always assures a specific starting position or condition.

According to yet a further modification, the head of the presser cheek having a U-shaped cross-section is supported by way of a widened T-shaped portion by a collar which extends transversely from the hollow member to either side of the head of this presser check. The support of the head of this presser cheek on the said collar may be effected by the interposition of a presser disc, acting as a load-bearing part.

In consequence of this form of construction it may be ensured, in a simple manner, that the associated presser cheek can be radially shifted or swivelled. Moreover, when a separate presser disc, for example a hardened presser disc, is used, a better stability and a longer service life are achieved.

Further, the presser cheeks and/or the slider wedge may have a hard metal lining in their lower contact portions. By reason of the appreciable forces which are entailed in the operation of splitting up rock and by reason of the necessary relative movements between the slider wedge and the presser cheeks large frictional forces are unavoidable in the regions of mutual engagement or contact, even when good lubrication is provided. For this reason the use of hard metal linings is, inter alia, to be highly recommended, because in this manner the service life of the different parts can be appreciably lenghtened.

Preferably, the slider wedge diverges in a plane extending perpendicularly of the plane in which it is tapered. This affords the advantage that, even when there is displacement of the slider wedge relative to the presser cheeks, there will always be sufficient contact between the presser cheeks and the foremost portion of the slider wedge.

BRIEF DESCRIPTION OF THE DRAWINGS Embodiments of the invention are hereinafter described, by way of example, with reference to the accompanying drawings, in which:

FIG. 1 is a longitudinal cross-section of the slider wedge and presser checks of a rock-breaking apparatus according to the invention;

FIG. 2 is a cross-sectional plan view taken along line ll-II in FIG. I;

FIG. 3 is a cross-sectional plan view taken along line llllll in FIG. I;

FIG. 4 is a cross-sectional plan view taken along line IV-IV in FIG. 1;

FIG. 5 is a cross-sectional plan view taken along line V-V in FIG. 1;

FIG. 6 is a cross-sectional side elevation taken along line Vl-VI of FIG. I, in which the slider wedge is not shown in cross-section;

FIG. 7 is a cross-sectional plan view taken along line VII-VII in FIG. 6; and

FIG. 8 is an elcvatlonal view of the two presser cheeks, one of which has been rotated through 90 relative to the other and is in the position which is assumed when the presser checks are being introduced.

DETAILED DESCRIPTION The longitudinal cross-sectional view of FIG. I illustrates the lower portion of an apparatus 10, for breaking up or splitting rock, in which a piston rod I2, which is preferably hydraulically actuated, engages with a slider wedge I4. This slider wedge engages between two presser cheeks I6 and 18 which project downwardly from within a hollow member 20. In use, when the piston rod is in its retracted position, the presser checks are inserted into a suitable drill hole, whereafter the slider wedge 14 is driven in consequence of the hydraulically generated axial force, between the presser checks. The presser checks are forced apart from one another, as a result of which the material surrounding the drill hole is broken up or split.

A guide sleeve 22, which serves to guide the piston rod 22, lies in the hollow member 20 which. in some suitable manner, is connected to a cylinder block (not shown), for example by screwing. The guide sleeve 22 has axially spaced end face portions and an intermediate disc 24 abuts against one of these end face portions and serves to transmit force between the two presser cheeks 16, 18. As shown in FIG. 1, the open end of the hollow member 20 is closed off by a resilient impact disc 26, but as shown in FIG. 6, this opening is defined by two inwardly directed shoulders 50 of the hollow member 2. Segment shaped plates 28 which serve as supports for the head 30 of the presser check 18 rest on these shoulders 50.

As becomes particularly clear from FIG. 5, the head 30 of presser cheek 18 is U-shaped in cross-section. The cross-section of the head 30 has a cross strip 34 and arms or shanks 36 which are attached to both sides of the cross strip 34. The arms 36 straddle the slider wedge I4 and also the head 38 of the other presser check 16. Above the plates 28 the head 30 of presser cheek I8 is widened as is clear from FIG. 5 so as to define the cross-bar 40 of a T-shaped portion 32 and the crossbar of the said T-shaped portion is supported on the two plates 28. As is particularly clear from FIGS. 1 and 6, presser cheek I8 is in this way axially located with the provision of only a small degree of play be tween the plates 28 and the intermediate disc 24.

As becomes clear from FIG. 8, the head 38 of the other presser cheek I6 is T-shaped in longitudinal cross-section. This head 38 is thus widened in its upper portion to define the cross-bar 40 which is connected to the remainder of the presser cheek I6 by a reduced neck portion 42 and there are shoulders 44 at the junction between the neck portion 42 and the remainder of the presser cheek I6.

During the course of assembly of the different parts of the apparatus, the presser check 18 is moved radially in the Iefthand direction (FIG. 1), whereby free space is created for permitting insertion of the presser cheek I6. In this way, the presser cheeks l6 and I8 assume their respective positions. as illustrated in FIG. 8, and the cross-bar 40 can, together with the neck portion 42 of the head 38 of presser check 16, be inserted between the arms 36 of the U-shaped head 30 of the presser cheek I8. Presser cheek I6 is then turned through so that the shoulders 44 lie under, and abut, the underface of the head 30 of presser cheek I8. The cross-bar 40 of the head of the presser cheek I6 lies above the intermediate disc 24, and rests on this disc 24. In this way the heads 30, 38 of the presser cheeks (and, consequently, the main bodies of the presser cheeks themselves) are locked one in the other and are axially located.

As can be seen from FIG. I, a radially projecting lug 46 of the head 38 of presser cheek I6 abuts, in the assembled condition of the parts, again the hollow member 20.

Accordingly, presser cheek 16 cannot move radially at this point. However, and as becomes clear from FIG. I, there is a free space between the T-shaped portion of the head 39 of the presser cheek I6 and the other side of the hollow member 20 which facilitates removal of the presser cheek I6 when the latter has been turned through 90. Otherwise, the arms 36 of the head 30 of the presser check 18 would have to be separated from one another by a greater distance. It is possible, by reason of the relatively small length of the cross-bar 40 of the head 38 of presser cheek 16, to move this cross-bar 40 when the presser cheek 18 has been tilted a sufficient distance and when the presser cheek 16 has been turnedthrough an opening 48 (FIG. 5).

In the embodiment illustrated, the slider wedge I4 is of asymmetrical construction, as are also the associated presser cheeks I6 and 18. At its upper end, the slider wedge I4 is connected to the piston rod 12 by means of a transversely extending pin 52 which extends transversely of the longitudinal axis. This transverse pin 52 is mounted, with a close fit, in the end portion of the slider wedge 14, and the two laterally projecting parts of the pin 52 engage in co-operating, elongate holes of the piston rod 12. The size and arrangement of the elongate holes are selected so that, when the piston rod 12 is being advanced from the cylinder head, the mutually adjacent end faces 54 of the slider wedge 14 and of the piston rod 12 abut one another. The result of this is a relatively large area of surface contact for transmitting the force necessary for rock splitting operation. When the piston rod 12 is being retracted, for drawing in the slider wedge 14, the transverse pin 52 will only be in contact with the end regions of the elongate holes. As at this time, the operative forces are not particularly great, a large area of mutual surface contact between the slider wedge 14 and the piston rod 12 is not required.

Conveniently, the lower, sliding contact surfaces of the presser cheeks l6 and 18 and the slider wedge 14 are provided with a hard metal facing 56, to reduce wear. This expedient is necessary on account of the high working pressures and forces which occur in practice.

The resilient impact disc 26, at the underside of the hollow member 20, at least partially surrounds the presser checks (or their heads 30 and 38) and, in addition to protecting the parts which lie within the hollow member 20, ensures that the presser cheeks l6 and 18 will be continuously urged into contact with the slider or thruster wedge 14.

ln the illustrated embodiment, in which the slider wedge 14 and the presser cheeks 16 and 18 are of asymmetrical construction, presser cheek 18 is shifted in the left-hand direction, as viewed in FIG. 1, when the piston rod 12 is moved outwardly from its associated cylinder. Meanwhile, the presser cheek 16 remains stationary, at least at its upper end, because its lug 46 con tinuously abuts against the hollow member 20. Also, when presser check 16 is being withdrawn for repairing it or replacing it by a thicker presser check 16 the other presser cheek l8 and the slider wedge 14 are radially pushed or tilted in the left-hand direction as viewed in FIG. I.

lt is evident, particularly from FIGS. 2 and 3 in conjunction with FIG. 1, that the arms 36 of the head 30 of the presser cheek 18 extend downwardly as far as the cross-section llllll. This gives the head 30 of presser check 18 great structural rigidity, which widens the range of practical use of the apparatus. Moreover, the U-shaped formation of the head 30 of presser cheek l8 enables this part to be of thin-wall construction, so that (see FIG. 1) the taper angle of the slider wedge can be relatively great, whereby the rock is separated by a relatively large amount for a given length of axial movement of the slider wedge.

While there has been shown what is considered to be the preferred embodiment of the invention, it will be obvious that modifications may be made which come within the scope of the disclosure of the specification.

What is claimed is:

1. Apparatus for mechanically breaking up or splitting rock, comprising a hydraulically actuatable pistoncylinder assembly, a slider wedge having inclined surfaces being connected to a piston rod extending from the piston of the piston-cylinder assembly, first and sec- 0nd presser cheeks having interlocking heads and complementary inclined surfaces, and a hollow member connected to the piston-cylinder assembly and surrounding said axially interlocking heads of said first and second presser cheeks disposed on opposite sides of the slider wedge for insertion in a drill hole and lateral separation as a result of sliding movement of said inclined surfaces of the slider wedge over complementary inclined surfacesof the presser cheeks, the head of the first pressure cheek being supported for lateral movement within the hollow member and having a U-shaped axial cross-section with the arms thereof straddling the slider wedge, and the head of the second pressure cheek having a T-shaped longitudinal cross-section with the cross-bar thereof resting on the head of the first pressure cheek and a reduced neck portion which is straddled by the arms of the U-shaped axial crosssection of the head of the first pressure cheek.

2. Apparatus as claimed in claim 1, comprising a disc, and a guide sleeve, said disc being inserted at a clearance between the head of said first pressure cheek and a first portion of an end face of a guide sleeve for guiding the piston rod so as to support the cross-bar of the T-shaped longitudinal cross-section of the head of the second presser cheek.

3. Apparatus as claimed in claim 2, the cross-bar of the T-shaped longitudinal cross-section of the head of the second presser cheek abutting against a second portion of the end face of the guide sleeve, said second portion being closer to the piston-cylinder assembly than the first portion.

4. Apparatus as claimed in claim 1, including shoulders being formed at the base of the reduced neck portion of the 'l shaped longitudinal cross-section of the head of the second presser cheek adapted to abut the underface of the head of the first presser check.

5. Apparatus as claimed in claim 1, including a lug being formed below the head of the second presser cheek abutting the hollow member so as to locate the head of the second presser cheek against radially outward displacement.

6. Apparatus as claimed in claim 1, said slider wedge and the lower portions of both said presser cheeks being of symmetrical construction.

7. Apparatus as claimed in claim 1, said slider wedge and the lower portions of both said presser cheeks being of asymmetrically construction.

8. Apparatus as claimed in claim 7, the inclined surface of the first presser cheek having a greater angle of inclination than the inclined surface of the second presser cheek.

9. Apparatus as claimed in claim 1, comprising a transverse pin pivotally connecting said slider wedge to said piston rod.

10. Apparatus as claimed in claim 9, the ends of the transverse pin extending laterally from the slider wedge and engaging in elongate holes formed in the piston rod.

11. Apparatus as claimed in claim 1, comprising a resilient impact disc partially blanking off the lower end of the hollow member, said resilient impact disc at least partially surrounding the presser cheeks and retaining the presser checks in contact with the slider wedge.

12. Apparatus as claimed in claim 1, the head of said first presser cheek having a widened portion which is supported on two inwardly directedshoulders formed on the hollow member.

tions of the inclined surfaces of the presser cheeks and the slider wedge having facings of hard material.

15. Apparatus as claimed in claim 1, the side edges of the inclined surfaces of the slider wedge being divergent.

i i i 

1. Apparatus for mechanically breaking up or splitting rock, comprising a hydraulically actuatable piston-cylinder assembly, a slider wedge having inclined surfaces being connected to a piston rod extending from the piston of the piston-cylinder assembly, first and second presser cheeks having interlocking heads and complementary inclined surfaces, and a hollow member connected to the piston-cylinder assembly and surrounding said axially interlocking heads of said first and second presser cheeks disposed on opposite sides of the slider wedge for insertion in a drill hole and lateral separation as a result of sliding movement of said inclined surfaces of the slider wedge over complementary inclined surfaces of the presser cheeks, the head of the first pressure cheek being supported for lateral movement within the hollow member and having a U-shaped axial cross-section with the arms thereof straddling the slider wedge, and the head of the second pressure cheek having a T-shaped longitudinal crosssection with the cross-bar thereof resting on the head of the first pressure cheek and a reduced neck portion which is straddled by the arms of the U-shaped axial cross-section of the head of the first pressure cheek.
 2. Apparatus as claimed in claim 1, comprising a disc, and a guide sleeve, said disc being inserted at a clearance between the head of said first pressure cheek and a first portion of an end face of a guide sleeve for guiding the piston rod so as to support the cross-bar of the T-shaped longitudinal cross-section of the head of the second presser cheek.
 3. Apparatus as claimed in claim 2, the cross-bar of the T-shaped longitudinal cross-section of the head of the second presser cheek abutting against a second portion of the end face of the guide sleeve, said second portion being closer to the piston-cylinder assembly than the first portion.
 4. Apparatus as claimed in claim 1, including shoulders being formed at the base of the reduced neck portion of the T-shaped longitudinal cross-section of the head of the second presser cheek adapted to abut the underface of the head of the first presser cheek.
 5. Apparatus as claimed in claim 1, including a lug being formed below the head of the second presser cheek abutting the hollow member so as to locate the head of the second presser cheek against radially outward displacement.
 6. Apparatus as claimed in claim 1, said slider wedge and the lower portions of both said presser cheeks being of symmetrical construction.
 7. Apparatus as claimed in claim 1, said slider wedge and the lower portions of both said presser cheeks being of asymmetrically construction.
 8. Apparatus as claimed in claim 7, the inclined surface of the first presser cheek having a greater angle of inclination than the inclined surface of the second presser cheek.
 9. Apparatus as claimed in claim 1, comprising a transverse pin pivotally connecting said slider wedge to said pistoN rod.
 10. Apparatus as claimed in claim 9, the ends of the transverse pin extending laterally from the slider wedge and engaging in elongate holes formed in the piston rod.
 11. Apparatus as claimed in claim 1, comprising a resilient impact disc partially blanking off the lower end of the hollow member, said resilient impact disc at least partially surrounding the presser cheeks and retaining the presser cheeks in contact with the slider wedge.
 12. Apparatus as claimed in claim 1, the head of said first presser cheek having a widened portion which is supported on two inwardly directed shoulders formed on the hollow member.
 13. Apparatus as claimed in claim 12, comprising a plate forming a load bearing member being disposed between the widened portion of the head of the first presser cheek and each inwardly directed shoulder of the hollow member.
 14. Apparatus as claimed in claim 1, the lower portions of the inclined surfaces of the presser cheeks and the slider wedge having facings of hard material.
 15. Apparatus as claimed in claim 1, the side edges of the inclined surfaces of the slider wedge being divergent. 